Local Ablative Strategies After Endovascular Radioembolization

As the median time to radiographic response ranges from 3-8 months in published data,
utilization of post-treatment PET/MRI dosimetry offers a powerful mechanism for immediate
(within 36 hours) prediction of lesions that are likely to fail radioembolization. This early
prediction enables a window for subsequent locoregional therapy prior to re-initiation of
systemic chemotherapy. The investigators propose to evaluate patients who are undergoing
radioembolization for mCRC using PET/MRI derived dosimetry obtained within 36 hours of the
radioembolization procedure. Patients with four tumors or fewer receiving an average dose
(Davg) less than 30 Gy will be candidates for subsequent locoregional therapy (stereotactic
body radiotherapy (SBRT) or microwave ablation). This strategy will ideally increase the
therapeutic index of locoregional therapies, particularly in the patient population who has
exhausted their options for systemic therapy.

After radioembolization, patients will be divided into 5 strata as per the protocol schema.
Patients who receive a Davg greater than 30 Gy in all hepatic lesions will be placed in
Stratum 1 and will not undergo subsequent therapy. Patients with four or fewer lesions
receiving a Davg less than 30 Gy will be placed in Strata 2, 3, or 4 based on distribution of
the underdosed lesions. Stratum 2 will be comprised of patients with four or fewer underdosed
lesions less than 3 cm which do not touch vasculature greater than 4 mm in size. Patients in
this stratum will receive percutaneous microwave ablation to the underdosed lesions. Stratum
3 will be composed of patients with 4 or fewer underdosed lesions that are not amenable to
microwave ablation by virtue of either size (greater than 3 cm) or proximity to hepatic
vasculature greater than 4 mm in diameter. These patients will be treated with SBRT to the
underdosed lesions. Patients with a combination of lesions some of which are amenable to
microwave ablation and some of which are not (due to either size or proximity to vasculature)
will be treated in Stratum 4 with a combined approach - microwave ablation to all lesions
which are amenable and SBRT to any remaining underdosed lesions. Finally, Stratum 5 will
consist of patients with more than 4 underdosed lesions or with disease progression; these
patients will be referred for further systemic therapy and are not candidates for further
locoregional therapy on study.

Inclusion Criteria:

- Diagnosis of colorectal carcinoma with intrahepatic metastases; limited extrahepatic
metastasis is allowed as long as the overall metastatic burden is hepatic dominant.

- Local surgical resection is not possible due to tumor or patient factors.

- Prior locoregional therapy is allowed if completed at least 2 weeks prior to
enrollment.

- Prior chemotherapy is allowed if stopped/completed at least 2 weeks prior to
enrollment.

- At least 18 years old.

- ECOG performance status ≤ 1.

- Scheduled to undergo radioembolization for treatment of intrahepatic metastases.

- Able to understand and willing to sign an IRB-approved written informed consent
document.

Exclusion Criteria:

- Child-Pugh score 8 or greater.

- ALT or AST ≥ 6 x ULN.

- Prior history of abdominal irradiation. Patients who have received prior pelvic
radiation for colorectal cancer are eligible; however, prior radiation treatment plans
must be reviewed prior to enrollment.

- Presence of any contraindications to MRI scanning.

- GFR < 30 ml/min/1.73m2 (if receiving contrast for MRI).

- Currently on dialysis (if receiving contrast for MRI).

- Prior allergic reaction to gadolinium-based contrast agents (if receiving contrast for
MRI).

- Pregnant or nursing. Women of childbearing potential must have a negative pregnancy
test within 14 days of study entry.

- Uncontrolled intercurrent illness including, but not limited to, ongoing or active
infection, symptomatic congestive heart failure, unstable angina pectoris, cardiac
arrhythmia, or psychiatric illness/social situations that would limit compliance with
study requirements.